California Institute of Technology (Caltech) researchers have identified part of the Martian surface that was once a delta where a river likely emptied into an ocean, according to a news release.
The ocean, if it ever existed could nearly covered Mars' northern hemisphere and stretched over one-third of the planet.
"Scientists have long hypothesized that the northern lowlands of Mars are a dried-up ocean bottom, but no one yet has found the smoking gun," says Mike Lamb, an assistant professor of geology at Caltech and a coauthor of the study, published July 12 in the Journal of Geophysical Research.
Lead author Roman DiBiase, a postdoctoral scholar at Caltech, said the finding did not prove the existence of an ocean, but provided the strongest evidence to date. The red planet's northern hemisphere is flat and has a lower elevation than the southern hemisphere, much like many ocean basins on Earth.
The research team used new high-resolution images from the Mars Reconnaissance Orbiter (MRO) satellite to study the 100-square-kilometer area believed to have once been a coastline.
The area in the photos, Aeolis Dorsa, is about 1,000 kilometers east of the Gale Crater, where Mars rover Curiosity has been exploring.
Scientists have discovered deltas on Mars before with most being inside a geological crater. Therefore, water most likely flowed into a lake, not an ocean.
"This is probably one of the most convincing pieces of evidence of a delta in an unconfined region-and a delta points to the existence of a large body of water in the northern hemisphere of Mars," DiBiase said.
There are other explanations for the latest delta discovery. For example, there could be a large geological boundary like a crater that was erased over time, Lamb suggested. The next step for the researchers is to continue examining the area most likely to be the coastline.
"In our work and that of others-including the Curiosity rover-scientists are finding a rich sedimentary record on Mars that is revealing its past environments, which include rain, flowing water, rivers, deltas, and potentially oceans," Lamb said. "Both the ancient environments on Mars and the planet's sedimentary archive of these environments are turning out to be surprisingly Earth-like."
